This work proposes to investigate the DNA damage and repair kinetics of rat brain tumors and normal brain tissue (cerebellar neurons) after irradiation in vivo. Slow reorienting zonal rotors will be used to evaluate size and structural changes in the DNA. A comparison of the DNA results with tumor cell survival may elucidate the mechanisms responsible for cell death and recovery. After single and split doses of radiation have been studied, optimum fractionation schedules for the treatment of malignant brain tumors will be devised and tested in animal model systems. BIBLIOGRAPHIC REFERENCES: Wheeler, K.T., Linn, J.D., Franklin, R. and Pautler, E.L.: Characterization of Large Mammalian DNA Species Sedimented in a Reorienting Zonal Rotor. Anal. Biochem. 64:329-342 (1975). Barker, M., Hoshino, T., Wheeler, K.T. and Wilson, C.B.: Chemotherapeutic Implication of Early Tumor Cell Proliferation in an Animal Brain Tumor Model. J. Nat. Cancer Inst. 54:851-853 (1975).